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Material development and process optimization of Laminated Object Modeling process

Authors Mak, Ka Yee
Issue Date 1998
Summary Laminated Object Modeling (LOM) is a commercial rapid prototyping technique. It builds a 3-D model by bonding double-layer structure laminates of prescribed cross-sections together under heat and pressure. A new composite has been designed and manufactured with a thickness and weight distribution of ~76±6.6 μm and 8.4±0.9 mg/mm2, respectively. This composite has a single-layer structure yielding improved mechanical integrity and resistance to compression. Experiments were conducted to investigate the effect of moisture, compressive creep deformation and the interactions between adhesive fracture energy and process conditions. The effect of moisture on the dimensional and geometric changes of conventional material and the new composite were examined. Warpage was observed only in conventional material because of the swelling difference between the cellulose and adhesive layer. The composite was found to exhibit a 75% swelling reduction in thickness when exposed to a humid environment. LOM composites eliminate this structural bias and hence it is more resistant to swelling warpage. Experiments were conducted to predict the thickness of LOM composite from the individual component deformation behavior, in terms of the processing time, temperature and pressure. From this study, a dramatic increase in strain was found at transition temperature of 45°C, such that the polymer was losing creep resistance to compressive loading. A governing creep equation for the LOM composite was established according to these experimental results. Simulation of a surface profile demonstrated that there was a shape distortion if conventional layer compensation method was employed. By applying the creep equation, the thickness of individual layer was predicted, hence, a better surface profile accuracy may be obtained. Peel tests were performed to characterize and optimize the bonding conditions in terms of adhesive fracture energy and deformation of the laminate. Consequently, a recommended process window has been derived which facilitates the tile detachment without damaging the LOM composite model. The recommended roller temperature was around 70°C, compressive load was supposed less than 500N and pressurized duration was one minute. The adhesive fracture energy calculated for the above settings was 26.9 J/m2 and the corresponding percentage thickness deformation was 15%. The feasibility and applicability of the LOM composite were evaluated by several case studies including a simple shape solid and a toy casing as prototypes. A complete manufacturing process from prototyping to metal part casting was established. It was found that the laser-cutting surface of the prototype and metal part surface made of LOM composite were smoother than those of the conventional material. More experiments can be conducted to explore more applications for the future RP development.
Note Thesis (M.Phil.)--Hong Kong University of Science and Technology, 1998
Language English
Format Thesis
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